Introduction to Biology

• Biology is the scientific study of life
• It encompasses the structure, function, growth, origin, evolution, and distribution of living organisms

Core Principles of Biology

• Cell theory: All living organisms are composed of cells
• Cells are the basic units of structure and function in living organisms
• All cells arise from pre-existing cells
• Gene theory: Traits are inherited through genes
• Genes are specific regions of DNA that code for particular traits
• Evolution: Life on Earth has evolved over time through a process of descent with modification
• Natural selection drives this process, favoring individuals with advantageous traits
• Homeostasis: Living organisms maintain a stable internal environment
• This is achieved through various regulatory mechanisms

Levels of Biological Organization

• Biosphere: The part of Earth inhabited by living organisms
• Ecosystem: A community of interacting organisms and their physical environment
• Community: Populations of different species living in the same area
• Population: A group of individuals of the same species living in the same area
• Organism: An individual living being
• Organ System: A group of organs working together to perform a specific function
• Organ: A structure composed of different tissues working together to perform a specific function
• Tissue: A group of similar cells performing a specific function
• Cell: The basic unit of life
• Organelle: A structure within a cell that performs a specific function
• Molecule: A group of atoms bonded together

Classification of Living Organisms

• Taxonomy is the science of classifying and naming organisms
• The current classification system includes:
  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

Three Domains of Life

• Bacteria: Prokaryotic, single-celled organisms
• Archaea: Prokaryotic, single-celled organisms that often live in extreme environments
• Eukarya: Eukaryotic organisms with cells containing a nucleus and other membrane-bound organelles
• Includes protists, fungi, plants, and animals

Key Biomolecules

• Carbohydrates: Provide energy and structural support
• Examples include sugars, starches, and cellulose
• Lipids: Store energy, form cell membranes, and act as hormones
• Examples include fats, oils, and steroids
• Proteins: Perform a wide variety of functions, including catalysis, transport, and structural support
• Composed of amino acids
• Nucleic acids: Store and transmit genetic information
• DNA and RNA are examples

Cell Structure and Function

• Prokaryotic cells: Lack a nucleus and other membrane-bound organelles
• Bacteria and archaea
• Eukaryotic cells: Contain a nucleus and other membrane-bound organelles
• Protists, fungi, plants, and animals
• Key organelles in eukaryotic cells:
• Nucleus: Contains the cell's DNA
• Mitochondria: Generate energy through cellular respiration
• Ribosomes: Synthesize proteins
• Endoplasmic reticulum (ER): Involved in protein and lipid synthesis
• Golgi apparatus: Modifies and sorts proteins
• Lysosomes: Break down waste materials
• Chloroplasts (in plant cells): Carry out photosynthesis

Energy and Metabolism

• Metabolism: The sum of all chemical reactions in an organism
• Catabolism: Breakdown of complex molecules into simpler ones, releasing energy
• Anabolism: Synthesis of complex molecules from simpler ones, requiring energy
• Enzymes: Catalyze biochemical reactions by lowering activation energy
• ATP (adenosine triphosphate): The primary energy currency of the cell

Photosynthesis

• The process by which plants and other organisms convert light energy into chemical energy
• Occurs in chloroplasts
• Involves two main stages:
• Light-dependent reactions: Convert light energy into chemical energy (ATP and NADPH)
• Light-independent reactions (Calvin cycle): Use ATP and NADPH to fix carbon dioxide and produce glucose

Cellular Respiration

• The process by which cells break down glucose to generate ATP
• Occurs in mitochondria
• Involves three main stages:
• Glycolysis: Breaks down glucose into pyruvate
• Krebs cycle (citric acid cycle): Oxidizes pyruvate to produce ATP, NADH, and FADH2
• Electron transport chain: Uses NADH and FADH2 to generate a proton gradient, which drives ATP synthesis

Genetics

• Genes: Units of heredity that determine traits
• DNA (deoxyribonucleic acid): The molecule that carries genetic information
• Double-stranded helix composed of nucleotides
• Nucleotides consist of a sugar, a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine)
• RNA (ribonucleic acid): Involved in protein synthesis
• Single-stranded
• Contains uracil instead of thymine
• Chromosomes: Structures that carry genes; composed of DNA and proteins
• Gene expression: The process by which genetic information is used to synthesize proteins

DNA Replication

• The process by which DNA is copied
• Ensures that each daughter cell receives a complete set of chromosomes
• Involves several enzymes, including DNA polymerase

Transcription

• The process by which RNA is synthesized from a DNA template
• Occurs in the nucleus
• Involves RNA polymerase

Translation

• The process by which proteins are synthesized from RNA
• Occurs on ribosomes
• Involves tRNA (transfer RNA), which carries amino acids to the ribosome

Cell Division

• Mitosis: Cell division that produces two identical daughter cells
• Used for growth, repair, and asexual reproduction
• Meiosis: Cell division that produces four genetically different daughter cells (gametes)
• Used for sexual reproduction
• Cell cycle: The series of events that take place in a cell leading to its division and duplication

Mendelian Genetics

• Gregor Mendel's laws of inheritance:
• Law of segregation: Each individual has two alleles for each trait, and these alleles separate during gamete formation
• Law of independent assortment: Alleles for different traits are inherited independently of each other

Evolution

• Evolution: Change in the genetic makeup of a population over time
• Natural selection: The process by which individuals with advantageous traits are more likely to survive and reproduce
• Mechanisms of evolution:
• Mutation: Changes in DNA sequence
• Gene flow: Movement of genes between populations
• Genetic drift: Random changes in allele frequencies
• Natural selection

Evidence for Evolution

• Fossil record: Shows the history of life on Earth
• Comparative anatomy: Similarities in the anatomy of different species indicate common ancestry
• Embryology: Similarities in the development of different species indicate common ancestry
• Molecular biology: Similarities in DNA and protein sequences indicate common ancestry
• Biogeography: The distribution of species on Earth reflects their evolutionary history

Ecology

• Ecology: The study of the interactions between organisms and their environment
• Population ecology: Studies the dynamics of populations, including birth rates, death rates, and migration
• Community ecology: Studies the interactions between different species in a community
• Ecosystem ecology: Studies the flow of energy and nutrients through ecosystems

Ecosystem Components

• Abiotic factors: Non-living components of the environment, such as temperature, water, and sunlight
• Biotic factors: Living components of the environment, such as plants, animals, and microorganisms
• Trophic levels: The position an organism occupies in a food chain
• Producers: Autotrophs that produce their own food through photosynthesis or chemosynthesis
• Consumers: Heterotrophs that obtain energy by consuming other organisms
• Decomposers: Break down dead organic matter

Biodiversity

• The variety of life on Earth
• Includes genetic diversity, species diversity, and ecosystem diversity
• Importance of biodiversity:
• Provides essential ecosystem services
• Supports human health and well-being
• Has intrinsic value
• Threats to biodiversity:
• Habitat loss
• Invasive species
• Pollution
• Climate change
• Overexploitation

Viruses

• Acellular infectious agents
• Consist of a nucleic acid genome (DNA or RNA) surrounded by a protein coat (capsid)
• Obligate intracellular parasites- require a host cell to replicate
• Viral replication involves attachment, penetration, replication, assembly, and release

Bacteria

• Prokaryotic, single-celled organisms
• Possess a cell wall, ribosomes, and a circular chromosome
• Reproduce through binary fission
• Play important roles in nutrient cycling, decomposition, and disease